They're Etruscan, but what are they?

Many people call them "vie cave": hollowed-out roads.
Here you see the beginning of the via cava di Poggio Cane.

A loose network of 15 obviously artificial rock cuts radiates outwards from the town of Pitigliano, including sections cut as much as 25 meters down thru rock: the chisel marks are visible everywhere. Not wide enough for a cart to pass comfortably, nor paved, nor even graded, they do sometimes include carved steps, and often what appear to be water channels: from one to four at any one place.

Whatever they are, there is general agreement that these "tagliate" (literally, "cuts") were carved out of the tufa by the Etruscans: occasional brief inscriptions have apparently been found, although I have seen none, and the illustrated books that speak of such do not show any. The cuts are not at all straight, as one might expect of a road; nor do they appear to lead anywhere in particular. A few tombs and caves give onto some of the vie cave, but they are hardly an essential characteristic of most.

A later Christian age seems to have felt a need to "baptize" many of these numinous places with crosses or attractive small shrines.

One of these shrines or edicole, in the via cava S. Giuseppe.

Needless to say, these gigantic works, up to a mile long, are a fertile field for theories, from the most mundane to the most esoteric: here general agreement is quite absent. I'm still sorting out my own ideas — temporarily, I think they might have been quarriesa — but a map and some more pictures will appear here from time to time.

A section of the via cava del Gradone.

Note:

a
Months after I wrote this I was delighted to be alerted to
this fascinating page of photos and text
describing a similar phenomenon in Malta, G.C., at the site of Misrah Ghar il-Kbir, identified by the authors as an ancient quarrying scheme.

Images with borders lead to more information.
The thicker the border, the more information.
(Details here.)